1) Field of the Invention
The present invention relates to a sequential segment joining type stator coil of an electric rotating machine (rotary electric machine) and a manufacturing method therefor.
2) Description of the Related Art
So far, there has been proposed a sequential segment joining type stator coil produced by sequentially joining many segment conductors inserted into slots of a stator core. For example, Japanese Patent No. 3118837 discloses a production of a sequential segment joining type stator coil in which joined sequentially are segments each forming a generally U-shaped electric conductor piece.
Further explaining it, for the production of this sequential segment joining type stator coil, a pair of leg portions of each of segments are individually inserted into a pair of slots separated from each other by approximately a magnetic pole pitch of a rotor and both the end portions thereof protruding therefrom are bent in circumferential directions, and the tips of both the leg sections of the respective segments are sequentially joined together.
That is, each of the segments is composed of a generally U-shaped (more accurately, a generally V-shaped) head portion (equally referred to as a “bent portion” or “turn portion”), a pair of slot electric conductors formed on both ends of the head portion and individually inserted into two different slots of a stator core from one side of the stator core in its axial direction, and a pair of protruding end portions formed on the tips of both the slot electric conductors to protrude toward the other side of the stator core in the axial direction and extend in its circumferential direction. The tips of the protruding end portions are joined by pairs. In the specification of the foregoing document, the slot electric conductors and the protruding end portions are equally referred to collectively as segment leg portions. Therefore, the head portion of each of the segments constitutes a head side coil end of a stator coil while the protruding end portions of each of the segments organize an end side coil end of the stator coil.
In addition, Japanese Patent No. 3118837 discloses that a total of four leg portions of a segment set comprising a small segment and a large segment surrounding this small segment are individually held in two rings located coaxially and these rings are relatively rotated to turn a pair of leg portions of each segment in a circumferential direction for the formation of head skewing portions.
Still additionally, Japanese Patent Laid-Open No. 2000-139049 discloses that a total of four leg portions of a segment set comprising a small segment and a large segment surrounding this small segment, each accommodated in a slot of a stator core, are individually held in four rings located coaxially and these rings are relatively rotated to turn a pair of leg portions of each segment in a circumferential direction for the formation of end skewing portions.
Yet additionally, Japanese Patent No. 3104700 discloses that, for a pair of end tip portions extending from four in-slot conductor portions adjacent to each other in a radial direction of a segment set and adjacent to each other in a radial direction thereof, basal electrode blocks are brought radially and outwardly into surface contact with radial-outside surfaces of the radial-outside end tip portion pair to bias this pair radially and inwardly, and radial-inside basal electrode blocks are brought into surface contact with radial-inside surfaces of the radial-inside end tip portion pair to bias this pair radially and outwardly, while a square-bar-like radial basal electrode extending radially is put in a circumferential spacing between the end tip portion pair adjacent to each other in a circumferential direction and a welding tip electrode is disposed close to axial tip surfaces of the end tip portion pair to be welded to weld the end tip portion pair.
A description will be given hereinbelow of an example of a manufacturing method for a sequential segment joining type stator coil disclosed in the above-mentioned documents and others.
First, the necessary number of pine-needle-like segments are prepared. Then, the pine-needle-like segments are processed into U-shaped segments and a pair of in-slot conductor portions of each segment are separated by approximately pole pitch from each other in a circumferential direction and a step is conducted so that the necessary number of segments are spatially disposed (arranged in a circumferential direction) to be simultaneously inserted into a slot of a core. In this step, for example, the rings with a plurality of holes disposed coaxially, shown in FIG. 3 of the above-mentioned Japanese Patent No. 3118837, are used and both leg portions of each of the pine-needle-like segments are individually inserted into the holes made in the corresponding circumferential positions of these hole-made rings and the rings are relatively rotated by an approximately pole pitch so that the pine-needle segment is processed into a U-shaped segment in which its head portion is spread circumferentially into a U-like (or V-like) configuration. Usually, this step is implemented with respect to a segment set comprising a small segment and a large segment.
As a subsequent step, each of the segments formed into a U-like configuration and aligned in a circumferential direction is inserted into the slot of the core. In this step, a head portion of each of the segments deformed into a U-like configuration and aligned in a circumferential direction is held while leg portions thereof are drawn out from the aforesaid pair of hole-made rings and are inserted into the slot of the core.
Following this, a step follows to bend protruding end portions protruding from the slot in a circumferential direction. Preferably, each of the protruding end portions is bent by the half of the pole pitch in the circumferential direction. Such circumferential bending can be made such that, for example, through the use of rings each having a plurality of holes and disposed coaxially, shown in FIGS. 4 and 5 of the above-mentioned Japanese Patent No. 3196738, the tips of the protruding end portions are inserted into the respective holes of the hole-made rings and each of the hole-made rings is rotated by the half of the pole pitch (electrical angle π/2) in a circumferential direction to bend each of the protruding end portions by the half of the pole pitch in the circumferential direction. In this connection, it is preferable that, in rotating each of the hole-made rings, the hole-made ring is directed at the protruding end portion and is rotated while being biased in an axial direction, for that this can enlarge the radius of curvature of the bending point. Then, a welding step follows to weld the tips of the respective protruding end portions in a predetermined sequence.
Thus, phase coils signifying coils of the respective phases are formed in an endless condition and a U-shaped head portion of each U-shaped segment is cut at an appropriate site, thereby forming outgoing terminals of each phase coil. If these outgoing terminals are made long in advance, when each of these long-made portions is bent in a circumferential direction, it can be used as a crossover for a neutral point. Incidentally, the reason that these outgoing terminals are located at the head side coil ends is that, in the case of the location at the end side coil ends, the long outgoing terminals interfere with the welding step.
The sequential segment joining type stator coil described above has so far been employed as a stator coil of an AC generator for vehicles.
However, the sequential segment joining type stator coil disclosed in the above-mentioned documents and others creates the following problems.
As mentioned above, Japanese Patent No. 3104700 proposes a welding technique in which, as shown in FIG. 14, a radial-outside basal electrode block 11x contact-feeds electricity to a radial-outside end tip portion pair 13x of a segment set while a radial-inside basal electrode block 10x contact-feeds electricity to a radial-inside end tip portion pair 13x of the segment set, and even these end tip portion pairs 13x are interposed between a pair of square-bar-like radial basal electrodes 12x for feeding electricity.
However, in the case of this conventional end tip portion pair welding technique, there are problems to be solved as mentioned below.
First, in the above-described conventional technique, there is a need to strongly press the radial-outside basal electrode to the radial-outside end tip portion pair and the radial-inside basal electrode to the radial-inside end tip portion pair, and this strong biasing force can displace or deform the radial-outside end tip portion pair toward the inside in a radial direction and, likewise, displace or deform the radial-inside end tip portion pair to the outside in a radial direction, which can cause poor welding due to the positional displacement or can shorten the spacing between these end tip portion pairs in a radial direction after welding to degrade the electrical insulating property therebetween. In this connection, the end tip portion pair is one-end-supported through end skewing portions by the stator core and the displacement or deformation of the end tip portion pair can easily occur due to elastic deformation or plastic deformation of the end skewing portions with a slot end surface of the stator core functioning as a supporting point.
On the other hand, the reduction of the aforesaid biasing force can deteriorate the insulating coat of the end skewing portions in the vicinity of the end tip portion pair due to a rise of the temperature of the basal electrode or the proximal portions of the end tip portion pair. Moreover, it can create a variation of the contact resistance voltage drop between the basal electrode and the end tip portion pair, which leads to an easy variation of a current flowing therethrough to result in welding finishes in dispersed conditions.
In addition, an electric rotating machine small in size, such as a vehicle AC generator conventionally known as an alternator, accepts such a turn configuration that one segment set, mentioned above, is disposed in a radial direction (four in-slot conductor portions are radially inserted into a slot) and, hence, as shown in FIG. 14, large-size radial-outside and radial-inside basal electrode blocks 10x and 11x can be disposed in a flee space to excellently reduce the resistance heat generation in the basal electrode, and the basal electrode blocks 10x and 11x carry out heat absorption to reduce the heat of the end tip portion pair 13x to be transferred from the proximal portions of the end tip portion pair 13x to an end skewing portion 14x with an insulating coat, thereby preventing the deterioration of the insulating coat.
However, in the case of a high-voltage motor such as a motor for driving a motor vehicle, it is expected that a large number of segment sets mentioned above are disposed in radial directions to increase the number of turns, and in this case, since it is not easy that the energization of the end tip portion pairs at intermediate positions in radial directions is made with a low resistance, difficulty is experienced in realizing a sequential segment joining stator coil type electric rotating machine with many turns, thus making it difficult to realize a high-voltage motor such as a vehicle driving motor.